Semiconductor structure with deep trench thermal conduction

ABSTRACT

Diodes and resistors for integrated circuits are provided. Deep trenches (DTs) are integrated into the diodes and resistors for the purposes of thermal conduction. The deep trenches facilitate conduction of heat from a semiconductor-on-insulator substrate to a bulk substrate. Semiconductor fins may be formed to align with the deep trenches.

FIELD OF THE INVENTION

The present invention relates generally to semiconductors, and moreparticularly, to semiconductor structures with deep trench thermalconduction and methods of fabrication.

BACKGROUND OF THE INVENTION

Diodes and resistors in an integrated circuit (IC) may be subjected tohigh voltages. For example, high voltages can develop in the vicinity ofan integrated circuit due to the build-up of static charges. A highpotential may be generated to an input or output buffer of theintegrated circuit, which may be caused, for example, by a persontouching a package pin that is in electrical contact with the input oroutput buffer. When the electrostatic charges are discharged, a highcurrent is produced at the package nodes of the integrated circuit, andis referred to as electrostatic discharge (ESD).

Regardless of the source of the high voltage, it is desirable to have adiode or resistor in an IC that is more resilient to high voltages.Furthermore, as both planar and fin-based technologies are prone todamage from high voltage, it is desirable to have a solution applicableto both technologies.

SUMMARY OF THE INVENTION

In one embodiment, a semiconductor structure is provided. Thesemiconductor structure comprises a bulk semiconductor substrate, aninsulator layer disposed on the bulk semiconductor substrate, asemiconductor-on-insulator layer disposed on the insulator layer, aplurality of deep trenches formed within the semiconductor structure,each deep trench of the plurality of deep trenches extending fromsemiconductor-on-insulator into the bulk semiconductor substrate, afirst terminal region formed on a perimeter region of the semiconductorstructure, a second terminal region formed on a central region of thesemiconductor structure, wherein a first subset of the plurality of deeptrenches is disposed within the first terminal region, and wherein asecond subset of the plurality of deep trenches is disposed within thesecond terminal region.

In another embodiment, a semiconductor structure is provided. Thesemiconductor structure comprises a bulk semiconductor substrate, aninsulator layer disposed on the bulk semiconductor substrate, asemiconductor-on-insulator layer disposed on the insulator layer, aplurality of deep trenches formed within the semiconductor structure,each deep trench of the plurality of deep trenches extending from thesemiconductor-on-insulator layer into the bulk semiconductor substrate,a gate ring disposed on the semiconductor structure, a plurality of deeptrenches disposed within the gate ring, a plurality of fins disposedwithin the gate ring and on the plurality of deep trenches, a firstterminal region formed within the gate ring, and a second terminalregion formed within the gate ring.

In another embodiment, a method of forming a semiconductor structure isprovided. The method comprises depositing an insulator layer on a bulksemiconductor substrate, depositing a semiconductor-on-insulator layeron the insulator layer, forming a plurality of deep trenches in thesemiconductor structure, and forming a gate ring on the semiconductorstructure, the gate ring delineating a central region and a perimeterregion, doping the central region with a first dopant type, and dopingthe perimeter region with a second dopant type.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation, and advantages of the present invention willbecome further apparent upon consideration of the following descriptiontaken in conjunction with the accompanying figures (FIGs.). The figuresare intended to be illustrative, not limiting.

Certain elements in some of the figures may be omitted, or illustratednot-to-scale, for illustrative clarity. The cross-sectional views may bein the form of “slices”, or “near-sighted” cross-sectional views,omitting certain background lines which would otherwise be visible in a“true” cross-sectional view, for illustrative clarity.

Often, similar elements may be referred to by similar numbers in variousfigures (FIGs) of the drawing, in which case typically the last twosignificant digits may be the same, the most significant digit being thenumber of the drawing figure (FIG). Furthermore, for clarity, somereference numbers may be omitted in certain drawings.

FIG. 1 is a top-down view of a diode in accordance with embodiments ofthe present invention.

FIG. 2 is a side view of a diode as viewed along line A-A′ of FIG. 1.

FIG. 3 is a side view of a diode as viewed along line B-B′ of FIG. 1.

FIG. 4 is a top-down view of a fin diode in accordance with embodimentsof the present invention.

FIG. 5 is a top-down view of a fin resistor in accordance withembodiments of the present invention.

FIG. 6 is a flowchart indicating process steps for embodiments of thepresent invention.

FIG. 7 is a flowchart indicating process steps for alternativeembodiments of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide improved diodes andresistors for integrated circuits. Deep trenches (DTs) are integratedinto the diodes and resistors for the purposes of thermal conduction.The deep trenches facilitate conduction of heat from asemiconductor-on-insulator substrate to a bulk substrate, making thedevices more resilient to heat generated from applied voltages andcurrents.

FIG. 1 is a top-down view of a diode 100 in accordance with embodimentsof the present invention. A semiconductor-on-insulator (SOI) structureis used to form the diode 100. As viewed top-down,semiconductor-on-insulator layer 102 is visible.Semiconductor-on-insulator layer 102 may be comprised of silicon. Aplurality of deep trenches (DTs), shown generally as 104, is formed inthe SOI structure. A deep trench is a trench with a depth greater thanits width, and may be a so-called “high aspect ratio” trench. A gatering 106 is disposed on the structure. Gate ring 106 may be comprised ofpolysilicon. The gate ring 106 may be formed via a sidewall imagetransfer (SIT) process. The gate ring 106 delineates a central region108 inside the gate ring, from a perimeter region 103 which is outsideof gate ring 106. The central region 108 is doped with a first dopanttype (e.g. N-type), and the perimeter region 103 is doped with a seconddopant type which is the opposite type (e.g. P-type). In someembodiments, the central region 108 may be doped P-type and theperimeter region 103 may be doped N-type. In embodiments, the P-typedopant species may be boron, and the N-type dopant species may bearsenic or phosphorous.

FIG. 2 is a side view of a diode 200 as viewed along line A-A′ ofFIG. 1. Bulk semiconductor substrate 210 forms the base of thestructure. Bulk semiconductor substrate 210 may be comprised of any ofseveral known semiconductor materials such as, for example, silicon,germanium, a silicon-germanium alloy, a silicon carbon alloy, asilicon-germanium-carbon alloy, gallium arsenide, indium arsenide,indium phosphide, III-V compound semiconductor materials, II-VI compoundsemiconductor materials, organic semiconductor materials, and othercompound semiconductor materials. Disposed above bulk semiconductorsubstrate 210 is insulator layer 212. Insulator layer 212 may becomprised of oxide, and may be referred to as a buried oxide (BOX)layer. Disposed on insulator layer 212 is semiconductor-on-insulator(SOI) layer 202. As stated previously, similar elements may be referredto by similar numbers in various figures (FIGs) of the drawing, in whichcase typically the last two significant digits may be the same. Forexample, semiconductor-on-insulator (SOI) layer 202 of FIG. 2 is similarto semiconductor-on-insulator (SOI) layer 102 of FIG. 1. A plurality ofdeep trenches, shown generally as 204, is formed within the diode 200.Each deep trench has a dielectric layer 231 disposed in a lower portionof the trench to provide electrical isolation between deep trench 204and bulk semiconductor substrate 210.

FIG. 3 is a side view of a diode 300 as viewed along line B-B′ ofFIG. 1. Gate ring 306 delineates a P-N junction within SOI layer 302.Regions 326 and 328 are terminal regions for the diode. The terminalregions for the diode may be either a cathode or an anode. A firstsubset of the plurality of deep trenches 304 is disposed within thefirst terminal region 326 and a second subset of the plurality of deeptrenches is disposed within the second terminal region 328. Inembodiments, an N+ region 328 forms a cathode of the diode. The N+region 328 is a heavily doped N+ region. In some embodiments, the N+region 328 has a dopant concentration ranging from about 1E18 atoms percubic centimeter to about 1E19 atoms per cubic centimeter. Inembodiments, a P+ region 326 forms an anode of the diode. The P+ region326 is a heavily doped P+ region. In some embodiments, the P+ region 326has a dopant concentration ranging from about 1E18 atoms per cubiccentimeter to about 1E19 atoms per cubic centimeter. The region 330directly under the gate ring 306 may be an N− region, which is a lightlydoped N-type region. In some embodiments, region 330 may have a dopantconcentration ranging from about 5E17 atoms per cubic centimeter toabout 9E17 atoms per cubic centimeter.

Two deep trenches, indicated generally as 304 are shown in this view.Each deep trench (DT) is filled with a conductor 335. In embodiments,conductor 335 may be comprised of polysilicon. Each DT comprises anupper region 323 which extends from SOI layer 302 through insulatorlayer 312, and lower region 324 which extends into bulk semiconductorsubstrate 310. The DTs have a depth that is greater than the width. Insome embodiments, the DTs may be “bottle-shaped” where the lower region324 has a first width W1 that is greater than a second width W2 for theupper region 323. The bottle shape may be formed by a variety oftechniques known in the industry, such as selective isotropic etching.In some embodiments, the DTs may have corrugated sidewalls to increasethe surface area of the conductor 335 against the bulk substrate 310.The interior surface of the DTs comprise an insulated region 320 that islined with a dielectric layer 331. Dielectric layer 331 may be a high-K(k>4) dielectric layer. In some embodiments, dielectric layer 331 iscomprised of hafnium oxide. In other embodiments, dielectric layer 331may be comprised of lanthanum oxide. Other materials for dielectriclayer 331 are possible. The dielectric layer 331 may be deposited viaatomic layer deposition (ALD), or other suitable method. In someembodiments, the dielectric layer 331 may have a thickness ranging fromabout 5 angstroms to about 20 angstroms. The dielectric layer 331extends from an intermediate point within the insulator layer 312, andextending to the bottom of each deep trench within bulk semiconductorsubstrate 310, and serves to electrically isolate the diode from thebulk semiconductor substrate 310. The DTs serve to transfer heat awayfrom the P-N junction of the diode and into the bulk substrate, enablingthe diode to accept more heat, and hence, higher currents and voltages.The DTs have an upper portion 322 where the dielectric layer 331 is notpresent, and where the trench conductor 335 is in direct physicalcontact with the SOI layer 302. While preferred embodiments utilize agate ring such as gate ring 306, it is also possible to use embodimentsof the present invention without a gate ring. For example, gate stripesmay be stretched across the silicon and used form the anode and cathodeof the diode.

FIG. 4 is a top-down view of a fin diode 400 in accordance withembodiments of the present invention. In this embodiment, a plurality offin structures 442 are formed on the SOI layer, and are disposed overdeep trenches 404. A merging semiconductor region 444 may be used tomerge the fins. The merging semiconductor region 444 may be comprised ofan epitaxially grown semiconductor such as epitaxially grown silicon orsilicon germanium. The gate ring 406 delineates a central region 408inside the gate ring, from a perimeter region 403 which is outside ofgate ring 406. In embodiments, a first epitaxial semiconductor region isin direct physical contact with the fins in the central region 408 and asecond epitaxial semiconductor region is in direct physical contact withthe fins in the perimeter region 403. The central region 408 is dopedwith one dopant type (e.g. N-type), and the perimeter region 403 isdoped with the opposite type (e.g. P-type). In some embodiments, thecentral region 408 may be doped P-type and the perimeter region 403 maybe doped N-type. In embodiments, the P-type dopant species may be boron,and the N-type dopant species may be arsenic or phosphorous.

FIG. 5 is a top-down view of a fin resistor 500 in accordance withembodiments of the present invention. Similar to fin diode 400 of FIG.4, fin resistor 500 comprises a plurality of deep trenches 504 formed ina semiconductor structure comprising a SOI layer, an insulator layer,and a bulk semiconductor substrate. A gate ring 506 is disposed on thesemiconductor structure. Unlike a diode, fin resistor 500 comprises afirst contact 548 and a second contact 550 that are both within the gatering 506. The contacts 548 and 550 may be comprised of polysilicon, orother suitable conductor. The deep trenches 504 are formed with asimilar structure to that shown in FIGS. 2 and 3, such that the deeptrenches are electrically isolated from the bulk semiconductorsubstrate. The resistance value of fin resistor 500 may be controlled byparameters such as dopant concentrations and/or length of the device.The deep trenches serve to transfer excess heat to the bulksemiconductor substrate, thereby increasing the resilience of the finresistor to elevated currents.

FIG. 6 is a flowchart 600 indicating process steps for embodiments ofthe present invention. In process step 650, a semiconductor-on-insulator(SOI) structure is formed, which comprises an insulator layer (e.g. BOXlayer) disposed on a bulk semiconductor substrate, and asemiconductor-on-insulator layer disposed on the insulator layer. Thesemiconductor-on-insulator layer is much thinner than the bulksemiconductor substrate. In process step 652, deep trenches are formed.This comprises recessing through the silicon-on-insulator layer andinsulator layer and into the bulk substrate. A dielectric layer isformed on the interior surface of the deep trench, and may then bepartially removed in the upper portion of the deep trench (see 322 ofFIG. 3). A conductor, such as polysilicon (see 335 of FIG. 3) is thendeposited in the deep trench. In process step 654, fins are formed inthe semiconductor-on-insulator layer. These fins may be formed usingtechniques known in the industry, such as patterning and recessing. Inprocess step 656, a gate ring is formed (see 406 of FIG. 4). The gatering may be comprised of polysilicon, and may be formed via a sidewallimage transfer (SIT) process. In process step 658, a P-N junction isformed by doping the central region (within the gate ring) with onedopant type (N-type or P-type), and doping the perimeter region (outsidethe gate ring) with the opposite dopant type.

FIG. 7 is a flowchart 700 indicating process steps for alternativeembodiments of the present invention. In this embodiment, the deeptrenches are formed after the fins (DT-last), whereas in the embodimentdescribed in FIG. 6, the deep trenches are formed prior to formation ofthe fins (DT-first). In process step 750, a semiconductor-on-insulator(SOI) structure is formed, which comprises an insulator layer (e.g. BOXlayer) disposed on a bulk semiconductor substrate, and asemiconductor-on-insulator layer disposed on the insulator layer. Thesemiconductor-on-insulator layer is much thinner than the bulksemiconductor substrate. In process step 752, fins are formed in thesemiconductor-on-insulator layer. These fins may be formed usingtechniques known in the industry, such as patterning and recessing. Inprocess step 754, deep trenches are formed. This comprises recessingthrough the fin and insulator layer and into the bulk substrate. Adielectric layer is formed on the interior surface of the deep trench,and may then be partially removed in the upper portion of the deeptrench (see 322 of FIG. 3). A conductor, such as polysilicon (see 335 ofFIG. 3) is then deposited in the deep trench. In process step 756, agate ring is formed (see 406 of FIG. 4). The gate ring may be comprisedof polysilicon, and may be formed via a sidewall image transfer (SIT)process. In process step 758, a P-N junction is formed by doping thecentral region (within the gate ring) with one dopant type (N-type orP-type), and doping the perimeter region (outside the gate ring) withthe opposite dopant type.

Although the invention has been shown and described with respect to acertain preferred embodiment or embodiments, certain equivalentalterations and modifications will occur to others skilled in the artupon the reading and understanding of this specification and the annexeddrawings. In particular regard to the various functions performed by theabove described components (assemblies, devices, circuits, etc.) theterms (including a reference to a “means”) used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (i.e., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary embodiments of theinvention. In addition, while a particular feature of the invention mayhave been disclosed with respect to only one of several embodiments,such feature may be combined with one or more features of the otherembodiments as may be desired and advantageous for any given orparticular application.

What is claimed is:
 1. A semiconductor structure comprising: a bulksemiconductor substrate; an insulator layer disposed on the bulksemiconductor substrate; a semiconductor-on-insulator layer disposed onthe insulator layer; a plurality of deep trenches formed within thesemiconductor structure, each deep trench of the plurality of deeptrenches extending from the semiconductor-on-insulator layer into thebulk semiconductor substrate, and wherein each deep trench is filledwith polysilicon; a gate ring disposed on the semiconductor structure,wherein a portion of the plurality of deep trenches is disposed withinthe gate ring; a plurality of fins disposed within the gate ring and onthe plurality of deep trenches; a first contact, formed within the gatering, disposed over and overlapping a first subset of the portion of theplurality of deep trenches disposed within the gate ring; and a secondcontact, formed within the gate ring, disposed over and overlapping asecond subset of the portion of the plurality of deep trenches disposedwithin the gate ring, wherein the first subset of the plurality of deeptrenches comprises at least two deep trenches, and wherein the secondsubset of the plurality of deep trenches comprises at least two deeptrenches.
 2. The semiconductor structure of claim 1, further comprisinga dielectric layer disposed on an interior surface of a lower portion ofthe deep trench, wherein the lower portion ranges from an intermediatepoint within the insulator layer and extending to the bottom of the deeptrench.
 3. The semiconductor structure of claim 2, wherein thedielectric layer disposed on an interior surface of a lower portion ofeach deep trench comprises hafnium oxide.
 4. The semiconductor structureof claim 1, wherein each deep trench is bottle-shaped.
 5. Thesemiconductor structure of claim 1, wherein the first contact and secondcontact are comprised of polysilicon.